Open Hole Casing Run Perforating Tool

ABSTRACT

Disclosed is an open-hole casing perforation tool having projecting fins around the circumference of a mandrel that have firing mechanisms and shape charges to allow flexible operation of geological formation fracturing at desired predetermined locations in an oil or gas well bore.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims benefit of Provisional Application Ser. No. 61/843,003 filed Jul. 4, 2013. The contents and disclosures of the application is incorporated herein by reference in its entirety for all purposes.

BACKGROUND

1. Field of Invention

This invention relates to an oil well perforating tool and methods in which explosive shape charges are activated by well pressure in order to fracture surrounding geological formations adjoining the well bore casings at predetermined locations.

2. Background

In the oil well drilling and completion industry hydrofracturing, or “fracing”, operations can be beneficial for a number of reasons. For example, fracturing operations help to stimulate the production of hydrocarbons from earth geological formations. In such operations, portions of the formation are fractured to increase fluid flow from the formation into a borehole. Fracturing generally includes isolating (as with packers) a portion of the borehole and pressurizing fluid therein to a pressure sufficient to cause a fracture in the formation. Boreholes may include both vertical and horizontal sections, such as long horizontal wells commonly used in shale gas and other tight formations. In recent years many methods have been used to allow multiple fractures to be induced along the length of a lateral section.

These wellbore fractures are initiated by applying pressure to the annulus of the wellbore once a sliding sleeve has been opened either hydraulically or with a ball. The only fractures that will occur are the ones where the formation is weaker in its natural state. These hydraulically induced fractures may not be in an area of the formation that has been determined to be the best locations for removing all or as much of the hydrocarbons. It should be common practice to explosively fracture well casings at preferred locations in the geological formations that are considered most promising. Open hole casing shock loading or perforating tools should be are used for such fracturing.

We disclose an improved pre-fracturing energetic tool and methods for using it.

SUMMARY

The apparatus (tool) of this invention allows perforations or shock loading to help allow induced fracture to be placed wherever it is determined to have the best results. Perforations are mechanically applied to the formation where needed compared to just using applied pressure to initiate a natural fracture. There is no limit to the number of tools that can be placed in a single stage (group of individual tools). By perforating the formation with multiple tools, the number of fractures is increased in the wellbore. Pumping pressures are reduced because the breakdown pressures of the formation have been reduced. Stage spacing can be lengthened by installing more perforating tools in a stage and reducing the number of open hole packers and reducing the risk of packer failure. Shorter fracing times are achieved due to reduced number of stages preformed.

DESCRIPTION OF THE FIGURES

The Figures represent embodiments of the invention and are not intended to be limiting of the scope of the invention.

FIG. 1 is a cutaway drawing of the tool of the invention to illustrate the internal components.

FIG. 2A is a partial end view of the tool of the invention. There can be as many or as few blades (fins) as is desired.

FIG. 2B is a partial end view of the tool of the invention. There can be as many or as few blades (fins) as is desired.

FIG. 3 is a transparent cutaway view illustrating the radial positions of the components of an embodiment of the invention.

FIG. 4 is a drawing that represents a tool of the invention as it would be run in a well hole before being threaded to a liner string.

FIG. 5 is a schematic drawing of a tool that is an embodiment of the invention.

FIG. 6 is an end view of the tool of FIG. 5.

FIG. 7 is a schematic drawing of a firing head component of the tool of FIG. 5.

FIG. 8 is an illustration of a typical down-hole perforating tool arrangement using three tools and a single frac sleeve in a shorter stage configuration.

FIG. 9 is an illustration of a typical down-hole arrangement using six tools and a single frac sleeve in a longer stage configuration.

DESCRIPTION

In broad aspect the invention is a geologic formation perforation (or energetic) tool that allows a formation to be pre-fractured (or shock loaded) prior to high pressure liquid hydro-fracture (fracing) and includes methods of employing the tool in geologic formation fracturing.

The tool comprises, a mandrel having a series of projections, fins, located around the outer circumference, at least one of which fins houses a firing head assembly that may be connected to a detonation means (such as detonating cord). The detonating means are connected to ignition port(s) on shape charges that may be located on the fins. The mandrel body may be constructed with threaded ends for threading into a casing string. It may also be enlarged to fit over the casing and attached to the casing by fitting the mandrel body over casing and securing it with locking rings or pins.

In general, most but not necessarily all, of the fins will have a firing head assembly disposed in it. The fins are oriented longitudinally, laterally, and/or helically in reference to the orientation of the casing string. The fins are preferable disposed on the mandrel body in a customary array such as shown in FIG. 1. However, they may also be disposed on a skeletal frame that slides over the conveyed casing and held in place with locking rings or other suitable means.

The shaped charges, if used, are, in most applications, located in a manner to explode outward of the mandrel surface into the geological formation. The charges may be positioned in the mandrel so that one or more of the shaped charges produce a jet that constructively interact—that is produces jets that intersect in the formation. In some applications one or more of the shaped charges may be directed inward towards the well to create an additional communication port between the wellbore and the annulus.

The firing head assembly may be configured to incorporate a time delay mechanism. The firing head assembly time delay means can be any suitable means, including but not limited to, a time delay fuse, a mechanical means, a hydraulic means, a delay mechanism that is configured to interact with a fracture treatment (injection into the well of high pressure water to fracture the formation), and a delay mechanism configured to preferentially orient banks of charges to fire in conjunction with a fracture treatment. The mechanism interacts with the fracture by providing delay that would detonate the charges during or after a fracing treatment operation has occurred.

The shaped charges may be of any type utilized in wellbore perforation. They be deep penetrating charges, big hole charges, punch charges designed for limited penetration, reactive liner technology charges or linear charges that produce slot shaped holes. These type charges are well known to those skilled in the art. For example there are Razor deep penetrating charges. Interactive charges are described in publications available at http://www.perf.com/publications/. See also http://www.perf.com/chart.

Schlumberger describes its PowerJet Omega™ charge at http://www.slb.com/services/completions/perforating/gun systems/hollow carrier/powerjet omega deep charge.aspx.

Halliburton describes a variety of shaped charges at http://www.halliburton.com/en-US/ps/wireline-perforating/wireline-and-perforating/perforating-services/shaped-charges/perforating-shaped-charges. It should be appreciated by those skilled in the art that the shock loading or perforating charges may be replaced with propellant or some other energetic materials to shock load the geological formation in a manner to induce initial fractures that the hydraulic fractures will follow. It is not always necessary to perforate the formation, shock loading will be sufficient to direct the hydraulic fracture. Shape charges may be too large for some open hole applications and other propellants can be effectively used. It will in some applications, be sufficient to fill the body of the tool with propellant that when detonated will provide the necessary shock loading.

Punch charges are also referred to as circulation charges and are selected for a specific tubing/casing thickness. Puncher charges are designed to minimize/avoid outer casing damage and loss of integrity. http://www.dynaenergetics.com/EN/shaped-charges/puncher-charges-en.html

In one embodiment the invention is a firing head assembly that comprises a pressure activated release mechanism, a firing pin, an initiator percussion unit that ignites a detonation means (such as a detonation cord), housed in a suitable body that can be attached to or disposed in fins of perforating tools in a configuration to allow the initiation of detonation of shape charges located in the fins. The firing head is preferably easily detachable from the tool, such as that shown at 240 in FIGS. 5 and FIG. 7. The pressure activated release mechanism may be a rupture disc, a shear pin retained firing system or other means that will be apparent to those skilled in the art. The pressure activation release mechanism has a preset pressure for release. In a single tool with a multiplicity of fins the preset pressure may be set at the same or different release pressure settings for the mechanisms on the individual fins. They may be set at different pressure settings for different fins. They may be set to fire at a given pressure thereby allowing control of the orientation of the perforation to the well bore. For example, If orientation and reset pressure of the firing assembly on the fins is known the operator can run at such pressure to only activate the desired fins such as only the fins orientated on the upper or lower half, or any combination thereof.

The firing heads may be modular and interchangeable from one tool assembly to another and they may be configured to allow different initiation means other than detonation cords such as transmission from another fin firing head assembly.

Referring to FIG. 1 the tool of an embodiment of the invention, 100, comprises a mandrel, 120, with couplings 110 A and B on each end, a series of projections (blades or fins), 112, disposed around the circumference of the mandrel. Disposed in each of the fins is a firing mechanism means 101, a shear screw, 102, mechanical blasting cap, 103, and a linear shape charge or a row of perforating shape charges (such as the Razor™ line of charges, see http://www.perf.com/razor/) 104, (see also FIG. 6). FIG. 2 shows a top and bottom view of the tool, 100, Illustrating the way the blades are disposed around the outside circumference of the mandrel. FIG. 4 is a perspective view of the tool, 100.

In another embodiment, shown in more detail in FIGS. 5-7, the tool comprises a mandrel 201, having a firing head assembly, 240, disposed on each a plurality of fins 204, located around the circumference of the mandrel. FIG. 6 is an end view of FIG. 5. FIG. 7 shows the components of the firing head. Item 242 is a reverse acting rupture disc, 244 is a shear pin, 246 is a firing pin, 245, is a firing head body that contains a firing pin. Item 248 is an initiator percussion that ignites the detonation cord 210 that in turn ignites the shape charges 206. The firing head assembly is an embodiment of the invention.

The tool firing head mechanism is activated by predetermined pressure (set point selected for the rupture disc). When the preset pressure is reached, rupture disc 242 burst in each of the assemblies, allowing increased pressure into the firing head sub-assembly 240. At approximately the same time (a slight delay is caused by shear pins 244 retaining the firing pin, 246) the firing pin begins to travel towards a percussion initiator 248. Upon impact of the percussion initiator, a detonator cord booster, 243, is ignited which in turn ignites the detonator cord, 210. The detonator cord passes underneath each shape charge ignition port (206) causing the charge to detonate. The charge bursts through the port plug 207 and into the geological formation.

In a given tool the pressure setting of the individual rupture disc settings may be set at different pressure levels as explained herein.

An important aspect of the tool of the invention (FIGS. 5-7) is the ability to assemble the tool with the least amount of risk as well as having a method of disassembly that does not involve destructive means, thus providing a tool with great design flexibility. The tool provides several options to make it well suited for many different applications and operations. The activation of the firing pin primarily relies on an accurate and precisely controlled pressure reactive device (burst disc). The pressure rating on the disc allows the tool to be set-up for many options. With the proper set-up of rupture discs a system can be held a constant annulus pressure (below the pressure that would be required to hydraulically fracture), and still successfully detonate all tools within a fracturing stage, either by precisely controlling the rupture disc rating for the burst discs or setting one rupture disc marginally lower than all others in either the remaining fins on a single tool or the remaining tools in a stage. The latter setup would utilize the pressure generated from the initial fin's detonation providing a delayed detonation of a majority of the charges. The tool also, preferably, uses a detachable firing head that contains the initiation mechanism that allows it to easily be replaced with other means of initiation. Those additional initiation methods can incorporate time delays and other improvements. The fin design itself can also be altered to best create various perforation patterns into the well bore. The design alterations include, but are not limited to, the orientation of the fins (longitudinally, laterally, or helically), the number of fins on a tool (only confined by the amount of available space in the well annulus), and which of fins are installed to the tool (as each fin is independent of the others). An additional feature, depending on the casing size and well bore geometry, is that the tool can be made as an integrated part of the casing string or as a slip over system held in place by lock collars.

Operation

In operation the tool is, for example, set in line inside a single stage of casing that contained two packers (142) and a sliding sleeve (144) (FIGS. 8 and 9). Once the sliding sleeve is actuated the tool is exposed to the now higher wellbore pressure. Once a high enough annulus pressure is reached, a firing pin held in place by shear screws or firing head assembly would release the pin, impact a detonator and finally ignite perforating shaped charge(s).

In an embodiment of the invention, the tool is activated by annulus pressure around a liner string. In FIG. 1 the firing piston (101) is held in place by shear screws (102) pinned higher than the bottom hole (wellbore) pressure. When the frac sleeve is actuated either by a ball or hydraulic pressure, the frac sleeve opens and pressure is allowed to enter into the annulus of the wellbore. When the frac pressure is increased above the bottom hole pressure, the firing piston (101) will shear free and slide through a polished bore and strike a mechanical blasting cap (103) which initiates the detonation of a linear or round shape charge (104) that are located in fins (112) that surround the circumference of the Tool. FIGS. 2 and 3 show end views of the tool shown in FIG. 1.

The method of which the first fin assembly would transfer detonation in a secondary fin is accomplished by means of a connection line that contains secondary detonation cord (see FIG. 6, item 145) thereby continuing a line of detonation transmission to a secondary fin or by means of a pressure retaining line that would use the blast pressure of the initial fin transferred through the pressure retaining line into the firing head assembly of the next fin.

The first tool that is set at the lowest activation pressure, when it is initiated at its designed pressure to detonate its shaped charges, creates blast pressure that will propagate through the annulus of the well and initiate the function of another similar tool in a stage; a secondary type tool inside the same stage. In a similar fashion if two separate stages have pressure communication between them the first tool's blast pressure is used to initiate a similar tool in another stage. Likewise the first tool's blasting pressure can be used to initiate the function of a different tool in a different stage.

The tool is configured to be included into a well casing string as shown in FIGS. 4, 8 and 9. FIGS. 8 and 9 illustrate how the tool may be deployed in oil or gas wells. Packers, 142, seal the space between them and that space constitutes a stage as the term is used herein. Item 144 is a sliding sleeve. The tools may be spaced as desired and located at predetermined location to achieve perforations in desired locations.

In the foregoing specification, the invention has been described with reference to specific embodiments thereof. It will, however, be evident that various modifications and changes can be made thereto without departing from the broader spirit and scope of the invention as set forth in the appended claims. The specification is, accordingly, to be regarded in an illustrative rather than a restrictive sense. Therefore, the scope of the invention should be limited only by the appended claims. 

1. A tool for perforating or shock loading a geological formation comprising: a mandrel, a series of projections, fins, located around the outer circumference of the mandrel, wherein at least one of the fins houses a firing head assembly.
 2. The tool of claim 1 wherein the ends of the mandrel are threaded to connect to a threaded end of casing or enlarged to be fitted over the end of casing and secured by locking rings or pins.
 3. The tool of claim 1 wherein the fins are oriented longitudinally, laterally, and helically in reference to the orientation of the casing string.
 4. The tool of claim 1 wherein the fins are disposed on a skeletal frame that is constructed to slide over a casing and is held in place with locking rings.
 5. The tool of claim 1 wherein shape charges are disposed in the fins and wherein one or more directed inward toward the well.
 6. The tool of claim 5 also comprising a detonation cord that is connected to ignition port(s) of shape charges located in a manner to explode in a predetermined direction.
 7. The tool of claim 5 wherein the shaped charges are selected from the group consisting of; deep penetrating charges, big hole charges designed for optimal hole size, punch charges designed for limited penetration, charges that incorporate reactive liner technology and linear shaped charges that produce slot shaped holes.
 8. The tool of claim 1 wherein the firing head assembly comprises a pressure activated release mechanism, a firing pin, an initiator percussion unit that ignites a detonation cord, housed in a suitable body that can be attached to fins of the perforating tools in a configuration to allow the initiation of detonation of shape charges located in the fins.
 9. The tool of claim 8 wherein the pressure activated release mechanism is a rupture disc or a shear pin retained firing system.
 10. The tool of claim 8 wherein the pressure activated release mechanism for each fin has a release mechanism set at a predetermined release setting that may be the same or different for individual fins.
 11. The tool of claim 8 wherein the pressure activated release mechanism is comprised of a reverse acting rupture disc.
 12. The tool of claim 8 wherein the firing head assembly is modular and interchangeable from one tool assembly to another and configured to be easily removable from the tool.
 13. The tool of claim 8 wherein the firing head assemblies are configured to allow interchange of initiation means.
 14. The tool of claim 8 wherein the firing head assembly also comprises a time delay means to delay the time from activation to release.
 15. The tool of claim 14 wherein the firing head assembly time delay means is selected from the group consisting of a time delay fuse, a mechanical means, a hydraulic means, a delay mechanism that is configured to interact with the fracture treatment, and a delay mechanism configured to preferentially orient banks of charges to fire in conjunction with the fracture treatment.
 16. A firing head assembly for a tool comprising a pressure activated release mechanism, a firing pin assembly, and an initiator percussion unit that ignites a detonation means.
 17. The firing pin assembly of claim 16 wherein the pressure release mechanism comprises a reverse acting rupture disc.
 18. The firing head assembly of claim 16 also comprising a shear pin located between the release mechanism and the percussion unit.
 19. A method of perforating or shock loading a geological formation comprising; providing a tool comprising a mandrel having a series projections, fins disposed around the outer circumference, wherein each projection houses a firing head assembly connected to a detonation means that is connected to an ignition port(s) of shape charges located in the projections in an manner to explode outward the mandrel surface, locating the tool in a desired location of a well casing; and activating the firing head assembly so as to initiate the shape charges.
 20. The method of claim 19 wherein the firing head assembly comprises a pressure activated release mechanism, a firing pin, an initiator percussion unit that ignites a detonation means, attached to fins of a tool in a configuration to allow the initiation of detonation of shape charges located in the fins.
 21. The method of claim 19 wherein the pressure activated release mechanism is a rupture disc and the activating means is pressure.
 22. The method of claim 19 wherein the firing head assembly has at least one firing initiator set at a lower activation level than the remaining assemblies so that when activated the pressure produced activated the remaining firing head assemblies;
 23. The method of claim 19 wherein there is a first and secondary firing assembly on separate fins and detonation is initiated in a secondary firing assembly by means of a secondary mechanism.
 24. The method of claim 23 wherein the detonation means is initiated in a secondary firing assembly by means of pressure transmission from a first firing assembly.
 25. The method of claim 19 wherein a plurality of perforating tools are arranged in one or more stages in which the tools are disposed in a casing string sealed by packers and wherein there is a first and second tool and wherein activation of a first tool acts to initiate the function of the second tool.
 26. The method of claim 19 wherein perforating tools are arranged in one or more stages in which the tools in each stage are disposed in a casing string sealed by packers and wherein activation of a first tool in one stage acts to activate a tool in another separate stage. 